[Cuis] Array2D newSize:

[Juan Vuletich]

Hi Dan,

On 7/15/2015 12:54 PM, Dan Norton wrote:
> Maybe it's my dyslexia, but isn't this backward?

It is not you. It is the unfortunate fact that 2 conventions exist for this

> "Array2D newSize: 2 at 3" produces an array with 3 rows and 2 columns:
> | nil nil |
> | nil nil |
> | nil nil |

Yes. 2 at 3 is a point with x=2 and y=3. x is usually regarded as the 
horizontal coordinate and y as the vertical coordinate. This is the 
universal convention for pixels in Displays and Forms and for 
mathematical points in the Cartesian plane.

> IMO it should be:
> | nil nil nil |
> | nil nil nil |

Yes. That's why Array2D class also has #height:width: and #width:height. 
Matrices are usually accessed with i, j; where i is the row and j the 
column. Array2D instances have #x:y: and #i:j: , and the order of the 
arguments is swapped. So you can pick the convention that bests suits 
what you are doing.

> For example, in Squeak, "MatrixTransform2x3 identity" produces: 
> MatrixTransform2x3(
> 1.0       0.0       0.0
> 0.0       1.0       0.0
> )

Yes. It uses the matrix convention.

> Please correct me if I'm wrong.
>
>  - Dan
>

  HTH.

In addition to all this Matrices have origin (1,1), while the 
mathematical plane and Forms have origin (0,0). But Matrices and Forms 
have the origin at the topLeft, while the mathematical plane has the 
origin at the bottomLeft (or at the center if you allow negative 
coordinates).

To make things even more complicated, when mapping the mathematical 
plane to a Form, you can map integer numbers in the plane to the center 
of the pixels (the convention that makes most sense to me) or to pixel 
corners (as Squeak / Cuis Rectangles do).

All unnecesary complications, but that we can't avoid.

Cheers,
Juan Vuletich
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